Monday, June 21, 2010

Summer Solstice

Just an observation about human nature ... but as a species, we seem to like to know funny little things about our world that don't directly impact our day-to-day life. And today is Summer Solstice, the "longest" day of the year. I think everyone knows that: that today, those of us in the northern hemisphere will experience the longest period of daylight of the year. From this point until Winter Solstice, the days get shorter and the nights get longer.

Everyone knows that. But slightly fewer people seem to remember that today is also the aphelion of the Earth's orbit around the sun. That's counter-intuitive to some, as in the northern hemisphere, it's warm right now, so we should be closer to the Sun, yeah? But then we remember that the tilt is much more significant than the distance from the sun. It's kinda like getting sunburned when skiing. Between the reflected rays from the snow and the thinner air at elevation, you're getting more sun exposure, even though the temps are hovering around freezing. Lots of factors, some are more significant than others.

I have found that even fewer people realize that Summer Solstice equates to the "slowest" days of the year. By slow, I mean, the earth's orbital velocity around the sun is the slowest. This might be easiest to explain by thinking of a tether ball. If you serve up a tether ball and watch it wind around the pole, it starts off relatively slow, but as the rope shortens and the orbital radius decreases, the ball appears to speed up. Similarly, when the earth is closest to the sun (on Winter Solstice), the orbital velocity is the fastest, but during the summer, our big blue globe is moving at it's slowest rate.

Because of inertia, the actual slowest day is around July 4th or 5th. Around New Year's, we're traveling at around 18.8 miles/sec, while on Independence Day, we're putzing about at around 18.2 miles/sec. (Either way, that's just over 65,000 mph.)

I guess folks don't remember this, or think about this, because we just can't relate. Longest and shortest days, those we can see, can feel. We plan our lives around the changing the of seasons, eating different foods at different times, even tailoring our holidays to match the prevailing conditions. That's why we don't grill hamburgers on Christmas Day, or decorate a pine tree to celebrate the signing of the Declaration of Independence. But relative orbital velocities ... well, we just can't "feel" that.

Maybe Corona should have a special ad campaign the first week of July: Slow it down on the slowest day of the year with a Corona. Copy needs some work, but there's a Science Meets Madison Avenue moment in there somewhere.

But like most things in life, it doesn't matter if you notice them or not ... they're still out there, happening, being, impacting your very being, in their own way, at their own pace.


tasteofbeirut said...

Thanks for enlightening us; I am afraid this is not the kind of thing that I know or seek out on my own, since I hardly even remember what the weather is like from day to day! But it is good and important to know.

oneordinaryday said...

This is such an interesting post. I didn't know much of what you shared, and I'm glad to find out.